The oxidative carbonylation of mono-olefins such as ethylene and propylene to prepare carboxylic acids and derivatives employing various catalyst systems, particularly noble metal catalysts is known; see for example, Fenton and Steinwand, Journal of Organic Chemistry, Vol. 37, 2034 (1972) as well as U.S. Pat. Nos. 3,397,226; 3,876,694; 3,907,882; 3,923,883; and 3,960,934.
In an article by Jiro Tsuji, Accounts of Chemical Research, Vol. 2, 144, (1969) and especially bibliographic references (36) and (37) noted therein, the carbonylation of preformed butadiene-isoprene-palladium chloride complexes in alcohol to give 1,4-dichloro-2-butene and ethyl 3-pentenoate and ethyl 5-ethoxy-3-methyl-3-pentenoate and dimethyl butyrolactone, with other minor products is described. In a related article by S. Hosaka and J. Tsuji, Tetrahedron, Vol. 27, 3821-3829 (1971) the palladium catalyzed carbonylation in alcohol of various conjugated dienes and the reaction mechanism are shown.
A recent Japanese Kokai No. 75,130714, Oct. 16, 1975, describes the preparation of carboxylic acid esters by reacting conjugated dienes, carbon monoxide and at least stoichiometric amounts and generally an excess of a monohydric alcohol in the presence of molecular oxygen and a Group 8 noble metal catalyst. Dehydrating agents may be used if necessary to maintain non-aqueous conditions.
While oxidative carbonylation reactions are generally known, the prior art does not show or describe the process of the present invention for the oxidative carbonylation of a diolefin, such as butadiene, to selectively prepare diene monoester employing a stoichiometric or greater, i.e., an excess amount of an enol ether or a 1-alkoxycycloalkene as reactant, which monoester, may be further processed by catalytic dimerization, catalytic hydrogenation and catalyzed hydrolysis reaction sequences to prepare pelargonic and sebacic acid and related derivatives. Catalytic dimerization of the monoester, methyl penta-2,4-dienoate, can provide fatty acid precursors. The diene monoesters of the instant invention are especially useful as difunctional monomers for the preparation of speciality block, graft, and other polymers.
The process of the present invention is directed to the preparation of a diene monoester by the catalytic oxidative carbonylation of a diolefin. More particularly, the instant process relates to the synthesis of monoesters by reacting carbon monoxide, oxygen, a diolefin such as 1,3-butadiene, isoprene, chloroprene and the like, and at least a stoichiometric amount of an enol ether such as 2-methoxypropene or a 1-alkoxycycloalkene such as 1-methoxycyclohexene, under elevated temperature and pressure conditions in the presence of a catalytic amount of a ruthenium, rhodium, palladium, osmium, iridium or platinum metal salt compound or mixtures thereof, and a copper (I), copper (II), iron (II) or iron (III) oxidant salt compound. Co-catalytic ligands or coordination complex compounds of the metal salt compounds and catalytic quantities of a primary, secondary or tertiary saturated alcohol, while not required in the process of the invention, may also be employed.
The process of this invention provides an economic process for the selective preparation of a diene monoester, which may be a monobasic fatty acid or sebacic acid precursor, by the oxidative carbonylation of a conjugated diolefin such as butadiene. There is provided a good conversion of the diolefin employed especially 1,3-butadiene, and excellent yield selectivity to the diene monoester. Carbonate esters, oxalate esters, carbon dioxide as well as other side reaction products associated with the oxidative carbonylation reaction are obtained in only trace amounts or eliminated by the reaction conditions employed in carrying out the process of the invention. The reaction is catalytic in both the platinum metal salt compound and oxidant salt compound and employs at least stoichiometric quantities of reactant diolefins, carbon monoxide, oxygen and/or air, and enol ether or a 1-alkoxycycloalkene. The reaction can be safely and conveniently carried out under a non-explosive oxygen or air/carbon monoxide atmosphere.